Thin film silicone rubbers and silicone-organic copolymers are finding increasing use in a wide array of sensing devices and other microelectronic devices packaged using standard semiconductor methodologies. One class of devices incorporating silicone-based materials is microassay sensing devices in which the silicone-based materials function as semipermeable membranes. Devices have been constructed whereby a silicone-based material overcoats the active region of a sensor, forming a semipermeable membrane between the sensor and the environment. The intrinsic selectivity and permeability of the silicone-based material regulates the flow of molecules to the active portion of the sensor and allows for a response of the sensor to only the desired analyte. In this way, analyte specific sensors can be constructed that can be used for chemically complex samples (such as blood, urine, or other biological samples) with a reduced observance of false responses.
One difficulty with incorporation of silicone-based materials in such a sensing device is the inability to directly pattern the films. In building the semipermeable membrane on the sensor, patterning of the silicone-based materials has traditionally required a multistep process where a patterning agent (such as a photoresist) is coated over the silicone-based film, the photoresist is dried, the photoresist is exposed to UV irradiation through a photomask, the patterned photoresist is developed, the selectively exposed underlayer of silicone-based material is solvent developed, and the remaining photoresist is stripped off. These processing steps to pattern the silicone-based material add complexity and cost to the process, require several material handling steps, and can frequently be identified as the source of device yield reduction.